The present invention relates to a safety valve apparatus for an air pressure operable diaphragm, and more particularly, relates to a safety valve apparatus for an air pressure operated diaphragm in which liquid such as chemicals (for example, medical liquid) can be prevented from leaking out of the diaphragm pump to contaminate a surrounding environment even if the diaphragm pump is damaged, and a service life of the diaphragm pump can be improved.
Generally, in some medical liquid plants, medical liquid supplied from a tank is supplied to a desired position by a diaphragm pump.
The diaphragm pump has, for example, a construction of a so-called double diaphragm type as shown in FIG. 1. In FIG. 1, a central rod 3 is disposed along an axis of a pump body 2 of a diaphragm pump 1 and is slidable in a left-and-right direction. By diaphragms 4 and 5, which are attached to both ends of the central rod 3, an inner chamber 6a and an outer chamber 7a, and an inner chamber 6b and an outer chamber 7b are defined at left and right sides, respectively. The pump body 2 cooperates with the central rod 3 to provide a switch valve function for switching an air flow direction. To this end, there are provided an air inlet port 8, an air outlet port 9, other air inlet and outlet ports 10, 11, a liquid flow-in port 12, a liquid flow-out port 13 and four check valves 14.
In operation, as shown by the arrow in FIG. 1, when compressed air from the air inlet port 8 enters the left inner chamber 6a through the port 10, since the left diaphragm 4 is pushed leftwardly, the central rod 3 is slid leftwardly, with the result that a volume of the outer chamber 7a is compressed. Accordingly, due to the presence of the check valves 14, liquid in the outer chamber 7a is pushed out upwardly in FIG. 1 and is forcibly flown out (or pumped out) through the liquid flow-out port 13. Meanwhile, air in the right inner chamber 6b flows into the atmosphere from the outlet port 9 through the port 11. Consequently, since the right outer chamber 7b is expanded to generate negative pressure, the liquid flows into the expanded chamber from the liquid flow-in port 12 through the check valve 14. Then, when compressed air from the port 11 enters the right inner chamber 6b, similarly, liquid in the outer chamber 7b is pushed out upwardly in FIG. 1 to be forcibly flown out (or pumped out) through the flow-out port 13. Meanwhile, liquid flows into the left outer chamber 7a through the flow-in port 12. In this way, the liquid is forcibly fed from the flow-in port 12 to the flow-out port 13 continuously, thereby pumping-out the liquid. Incidentally, a tank (not shown) has a predetermined (water) head with respect to the liquid flow-in port 12 of the diaphragm pump, and thus constant liquid pressure from the tank always acts on the flow-in port 12.
Now, a switching operation for the sliding direction of the central rod 3 will be explained with reference to FIG. 2. As shown in FIG. 2, when the central rod 3 is slid to the left to reach a left slide limit position while pushing the liquid out of the left outer chamber 7a by the action of the diaphragm 4, the diaphragm 4 is deformed to an outwardly convex configuration 4a under the action of the compressed air in the left inner chamber 6a. Immediately after that, since both the supply of the compression air to the right inner chamber 6b (FIG. 1) and the discharge of the compressed air from the left inner chamber 6a are started, the central rod 3 starts to be slid rightwardly, with the result that the liquid from the tank starts to be sucked into the left outer chamber 7a. However, this creates the following problems.
1 In FIG. 2, when the central rod 3 starts to be slid rightwardly, i.e., when a liquid sucking stroke for the left outer chamber 7a is started, since the constant liquid pressure from the tank becomes to act on the left outer chamber 7a, as air pressure in the left inner chamber 6a is reduced, the diaphragm 4 is suddenly reversed toward the inner chamber 6a (i.e., air chamber) to assume a reverse configuration 4b as shown by the broken lines in FIG. 2. During the continuous operation of the pump, if this phenomenon is repeated, fatigue of the diaphragm will be increased or the diaphragm will be damaged, with the result that the service life and reliability of the pump will be detrimentally affected.
2 If the diaphragm is damaged for the reason as mentioned in the above item 1 or other reason, since the outer chamber 7a and the inner chamber 6a would communicate with each other, the liquid acting on the flow-in port 12 with the constant pressure leaks from the air outlet port 9 through the check valve 14, outer chamber 7a, inner chamber 6a and air flow passage to the exterior, thereby contaminating the surrounding environment.
A first object of the present invention is to provide a safety valve apparatus for an air pressure operable diaphragm in which a diaphragm of a diaphragm pump can be reciprocated while maintaining an outwardly convex configuration, and, accordingly, the service life and reliability can be improved without generating the fatigue or crack in the diaphragm.
A second object of the present invention is to provide a safety valve apparatus for an air pressure operable diaphragm in which, even if a diaphragm of a diaphragm pump is damaged for any reason, the pressure in the liquid chamber is brought to atmospheric pressure, and the liquid flow-in port of the safety valve apparatus is immediately closed to block the further flowing-out of the liquid from the diaphragm pump to the exterior, thereby preventing the danger of contaminating the surrounding environment, while maintaining a clean environment.